Average probability of packet error with diversity reception over arbitrarily correlated fading channels

Closed form expressions for the average probability of packet error (PPE) are presented for no diversity, maximum ratio combining (MRC), selection combining (SC) and switch and stay combining (SSC) diversity schemes. The average PPE for the no diversity case is obtained in two alternative expressions assuming arbitrarily correlated Nakagami and Rician fading channels. For the MRC case, L diversity branches are considered and the channel samples are assumed to follow Nakagami distribution and to be arbitrarily correlated in both time and space. For the SC diversity scheme with L diversity branches, two bounds on the average PPE are derived for both slow and fast fading channels. The average PPE in this case is obtained in an infinite integral form for Nakagami channels while it is reduced to a closed form expression for the Rayleigh case. The average PPE is also derived in the case of SSC diversity with dual branches for both slow and fast Rayleigh fading channels. The new formulas are applicable for all modulation schemes where the conditional probability of error has an exponential dependence on the signal‐to‐noise ratio. The average PPE is then used to obtain a modified expression for the throughput for network protocols. In general, the diversity gain exhibits a little diminishing effect as the number of diversity branches increases. In addition, the system is found to be more sensitive to the space correlation than to the time correlation. The effects of different system parameters and diversity schemes are studied and discussed. Specific figures about the system performance are also provided. Copyright © 2004 John Wiley & Sons, Ltd.     

Analysis of packet loss in transport layer over ATM networks

In asynchronous transfer mode (ATM) networks, when cells are lost due to congestion, packets containing the lost cells should be retransmitted in the transport layer, which manages the end-to-end communication. The probability that a packet contains at least one lost cell depends on the packet length. It is thus very likely that the performance of the end-to-end communication is influenced by the packet length. In this paper, we analyse packet loss probability and the achievable maximum throughput when a block of data is divided into packets of fixed size and the lost packets are retransmitted based on the selective repeat automatic repeat request (ARQ). Through this analysis, we examine the effect of packet length and peak cell transmission rate on the performance measures mentioned above. © 1997 John Wiley & Sons, Ltd.     

无感知分组丢失下的无线传感器网络链路质量评估模型

针对现有链路质量评估方法没有考虑到不完整分组对链路产生的影响,将无线传感器网络的链路分组丢失分为感知分组丢失和无感知分组丢失,分析了无感知分组丢失产生的原因,在对无感知分组丢失进行度量的基础上,提出一种无感知分组丢失下的链路质量评估模型。该模型采用卡尔曼滤波对获取的CCI进行降噪处理,基于Cubic模型、最小二乘法拟合出CCI与无感知分组丢失率的关系模型。实验结果表明,无感知分组丢失下的链路质量评估模型是合理的,通过该模型求得的无感知分组丢失率与实测值接近。     

CCI-based link quality estimation mechanism for wireless sensor networks under non-perceived packet loss

This paper proposes a chip correlation indicator (CCI)-based link quality estimation mechanism for wireless sensor networks under non-perceived packet loss. On the basis of analyzing all related factors, it can be concluded that signal-to-noise rate (SNR) is the main factor causing the non-perceived packet loss. In this paper, the relationship model between CCI and non-perceived packet loss rate (NPLR) is established from related models such as SNR versus packet success rate (PSR), CCI versus SNR and CCI-NPLR. Due to the large fluctuating range of the raw CCI, Kalman filter is introduced to do de-noising of the raw CCI. The cubic model and the least squares method are employed to fit the relationship between CCI and SNR. In the experiments, many groups of comparison have been conducted and the results show that the proposed mechanism can achieve more accurate measurement of the non-perceived packet loss than existing approaches. Moreover, it has the advantage of decreasing extra energy consumption caused by sending large number of probe packets.     

一种基于捕获的扩频分组无线网MAC层协议及其性能分析

在分组接入过程中,当每个用户终端以随机竞争的方式获得所需的频谱资源时,会引起用户间的冲突和资源的浪费,造成系统性能的降低。本文引入了一种基于捕获的接入方法,当一个时隙中存在多个干扰分组时,该方法仍有捕获到某个分组的可能,该方法在系统高负载的情况下能有效地利用资源。性能分析和计算结果表明,基于捕获的方法改善了系统的性能。     

短程脉冲无线信道特性仿真与分析

利用仿真语言对短程脉冲无线信道进行仿真研究。考虑短程脉冲无线传播环境为具有某一密度的随机分布的散射体,在一种理想情况下,信道传播环境表现为一个渗透网格。利用仿真语言仿真短程脉冲无线信道中多径分量的传播轨迹,通过脉冲无线信道的随机模型对短程脉冲无线信道特性进行仿真分析,仿真结果表明：利用该模型对短程脉冲无线信道仿真是有效的。     

多速率系统呼叫级和分组级的损失率分析

对提供多速率实时VBR业务的系统中呼叫级和分组级的主要性能指标的分析计算进行了深入研究,从多维Markov链的全局平衡条件出发,提出了一种计算在部分共享策略下各业务在线连接数的联合概率分布的方法,在此基础上可算出呼叫损失概率和分组丢失率,仿真结果表明了其准确性。     

End‐to‐end delay and packet drop rate performance for a wireless sensor network with a cluster‐tree topology

In this paper, we study the delay performance in a wireless sensor network (WSN) with a cluster‐tree topology. The end‐to‐end delay in such a network can be strongly dependent on the relative location between the sensors and the sink and the resource allocations of the cluster heads (CHs). For real‐time traffic, packets transmitted with excessive delay are dropped. Given the timeline allocations of each CH for local and inter‐cluster traffic transmissions, an analytical model is developed to find the distribution of the end‐to‐end transmission delay for packets originated from different clusters. Based on this result, the packet drop rate is derived. A heuristic scheme is then proposed to jointly find the timeline allocations of all the CHs in a WSN in order to achieve the minimum and balanced packet drop rate for traffic originated from different levels of the cluster tree. Simulation results are shown to verify the analysis and to demonstrate the effectiveness of the proposed CH timeline allocation scheme. Copyright © 2012 John Wiley & Sons, Ltd.     

MIMO信道的GBDB模型及其信道容量分析

针对非频率选择性Rice衰落MIMO移动信道，建立GBDB模型，并推导出新的MIMO系统的GBDB模型的空时联合相关函数。新的GBDB模型统一现有的多种MIMO信道模型，新的空时联合相关函数综合考虑了无线衰落信道收发两端的多普勒扩展、非均匀角度扩展以及平均发射与到达方向，综合考虑了收发端天线阵的配置。最后基于新的空时联合相关函数，分析了非均匀散射参数以及Rice分布参数变化对MIMO信道统计容量的影响。     

小波包分析在故障特征提取与识别中的应用

对观测信号进行小波包分析,从而提取故障信息,建立能够表征系统特征的状态向量,用模式识别的方法对系统进行故障检测与定位,实现系统的故障诊断。     

A Model for the Performance Evaluation of Packet Transmissions Using Type-II Hybrid ARQ over a Correlated Error Channel

Type-II Hybrid-ARQ (Type-II HARQ) has been shown, under certain circumstances, to increase the efficiency and reduce loss of data transmissions over a wireless channel. However, it is difficult to predict how it will perform when transmission symbol errors are correlated. We present a computationally efficient approach to the performance evaluation of packet transmissions over a wireless link employing Type-II HARQ error mitigation when the physical channel is subject to correlated transmission symbol errors. This provides a tool for static or online optimization of system parameters. We present numerical results for a wide range of channel statistics, illustrating the effect of bit error correlation, bit error rate, and block size on packet latency and loss rate.     

一种FDL和LRWC相结合的光分组交换网络的性能分析

研究了FDL和有限长波长转换器(LRWC)相结合的方法来解决异步变长的分组交换网中的冲突问题,对这种冲突解决方案建立了数学模型并进行了理论分析,提出了一个用于修正最佳延迟单元的公式,即在负载较大的情况下,我们要求延迟单元较小,这样可显著的降低在此交换网中的分组丢失率;对系统丢包率与负载、FDL数目和最佳延迟单元的关系进行了研究和讨论,结果表明:在同样的输入负载情况下,有限长波长转换器(LRWC)的引入可以降低缓存的数量;对延迟单元的修正可以大大降低丢包率,同时系统的性能较之单独使用FDL时有较大的改善。     

Asymptotic analysis of multi‐branch EGC and SC over equally correlated Rician channels

Closed‐form asymptotic expressions for bit error rate and outage probability are derived for multi‐branch equal gain combining and selection combining receiver diversity over equally correlated Rician channels. Numerical results indicate that these analytical solutions can provide accurate estimation of bit error rate and outage probability in large signal‐to‐noise ratio regimes. The analytical results reveal some important insights into the performance characteristics of equal gain combining and selection combining diversity operating over equally correlated Rician fading channels. Copyright © 2013 John Wiley & Sons, Ltd.     

A flexible MAC protocol for the integration of high- and low-quality video streams, voice and data traffic over high-speed packet switched wireless networks

In this work, we propose and evaluate mechanisms for the multiplexing and the integrated delivery of various traffic types such as video, data and voice, over a wireless cellular high-speed packet switched network. Two different scenarios are examined where the video traffic results from videoconference sessions and high-quality media playback, respectively. In both cases we focus on the uplink channel and we thoroughly investigate, by using actual MPEG-4 video streams, the system's performance under a variety of possible loads. Our goal is to achieve high-aggregate channel throughput while preserving the quality of service requirements of each traffic type.     

An approximation and its applications in wireless networks performance analysis

In the literature, there are two common assumptions for the tele‐traffic parameter in analyzing the wireless network performance, that is, the tele‐parameter follows a specific probability density function (pdf) and additionally the pdf exists closed‐form Laplace Transform (LT). However, taking into account the cell irregular shape, the specific pdf may be unavailable while only the measured statistical moments are available. Moreover, the pdf function may not exist a closed‐form LT, for example, lognormal distribution function. In this paper, based on the Central Limit Theorem and hyper‐Erlang universal approximation property, we propose an approximation method applicable in the situations when only the statistical moments are available or LT of pdf does not exist. We then employ the technique in diverse applications, including the performance analysis of wireless network and the cost evaluation of mobility management. Extensive numerical examples demonstrate the good approximation capability to the exact formula and the simulation results. Copyright © 2006 John Wiley & Sons, Ltd.     

An improvised indexing technique for XML data over multiple channels in wireless environment: (1, Xm) method

Wireless broadcasting is the new emerging standard for disseminating the information. It also exploits the feature of mobile computing environment, i.e., an asymmetric environment where the bandwidth of downloading is much higher than the bandwidth of uploading. Due to the small devices, created to hold the feature of portability, various difficulties are imposed on the system. The mobile client follows some energy restricted traits to be efficient. Those traits are access time and tuning time. Access time basically tells the efficiency of the system by specifying how fast a user may get data. But tuning time measures the battery life of the device. In this paper, we have proposed (1, X_m) method to deal with these. Here, X_m basically implies the XML data passing on to the multiple channels. In this technique, we have sent data by indexing onto two different channels: index and data channel. We have analyzed the performance of the proposed indexing technique. To prove its validity, the improved results are compared with the former indexing techniques analytically and experimentally.     

一种高效的无线数字通讯的SoC设计方法及其在无线局域网芯片设计中的应用

介绍一种针对高性能的无线数字通讯系统的SoC设计方法。该方法对SoC设计要求高效合理地进行软硬件划分,将划分后的硬件子模块映像到一个高效的多通道总线拓扑结构中以及为不同通道的本地总线设计一个高效自适应的访问协议。同时提出一种全新的专门针对SoC设计、基于总线监控的高效实用的可测性设计方案。以这些设计方法为指导,文章为IEEE 802.11无线局域网的介质访问层和基带控制层的SoC芯片设计提出了一个系统参考解决方案。     

Outage analysis in wireless channels with multiple interferers subject to shadowing and fading using a compound pdf model

Wireless communication systems are subject to short- and long-term fading of the channel. Instead of the commonly used Nakagami–lognormal model to account for the conditions existing in these shadowed fading channels, a compound probability density function (pdf) model is used to evaluate the performance of wireless systems. While the Nakagami–lognormal lacks a closed-form solution to the pdf of the received power in shadowed fading channels, the compound pdf has an analytical expression for the pdf of the received signal power. The synergy between these two models for the analysis of wireless systems is explored by calculating the bit error rate in a DPSK modem as well as the outage probability in a wireless system in a shadowed fading channel. This is followed by the computation of the outage probability in the general case where both the desired and cochannels are subject to shadowing and fading. The analyses were carried out for both fixed number of cochannels and random number of cochannels. Results demonstrate the usefulness of the compound pdf model for the performance analyses of wireless systems in shadowed fading channels.     

Diversity‐multiplexing tradeoff over correlated Rayleigh fading channels: a non‐asymptotic analysis

In this paper, we present a finite‐signal‐to‐noise ratio (finite‐SNR) framework to establish tight bounds on the diversity‐multiplexing tradeoff of a multiple input multiple output (MIMO) system. We focus on a more realistic propagation environment where MIMO channel fading coefficients are correlated and where SNR values are finite. The impact of spatial correlation on the fundamental diversity‐multiplexing tradeoff is investigated. We present tight lower bounds on the outage probability of both spatially uncorrelated and correlated MIMO channels. Using these lower bounds, accurate finite‐SNR estimates of the diversity‐multiplexing tradeoff are derived. These estimates allow to gain insight on the impact of spatial correlation on the diversity‐multiplexing tradeoff at finite‐SNR. As expected, the diversity‐multiplexing tradeoff is severely degraded as the spatial correlation increases. For example, a MIMO system operating at a spectral efficiency of R bps/Hz and at an SNR of 5 dB in a moderately correlated channel, achieves a better diversity gain than a system operating at the same spectral efficiency and at an SNR of 10 dB in a highly correlated channel, when the multiplexing gain r is greater than 0.8. Another interesting point is that provided that the spatial correlation channel matrix is of full rank, the maximum diversity gain is not affected by the spatial correlation. Copyright © 2009 John Wiley & Sons, Ltd.     

风机绕射损耗估算方法及对电子系统影响的分析

针对风力发电机对电磁波产生的绕射效应,提出风力发电机绕射估算适用有限宽度屏蔽的绕射损耗计算模型;通过刀刃形障碍物绕射损耗估算方法和有限宽度的屏蔽绕射损耗估算方法,可以得出风力发电机绕射损耗估算值,并据此进行了仿真计算。计算表明位于雷达覆盖扇区内的风力发电机绕射损耗会导致雷达漏警率和虚警率的提高。